Golf ball

ABSTRACT

A golf ball includes a solid core, and a cover having one layer or two or more layers provided to directly cover the solid core or cover the solid core via an intermediate layer. At least one layer of the cover is taken as a high hardness cover layer which is made from a base resin containing an inorganic filler in an amount of 5 to 40 parts by weight on the basis of 100 parts by weight of the base resin and which has a Shore D hardness in a range of 66 to 80. With this configuration, the golf ball can exhibit a high carrying performance, a desirable very soft feeling of hitting, and an excellent durability against continuous hitting.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a golf ball capable of giving a soft feeling of hitting the ball to a golf player, and enhancing the carrying performance of the ball.

[0002] In recent years, soft golf balls for giving soft feeling of hitting the balls to golf players have been increasingly required. Such soft golf balls, however, have also been required to have a high resilience enough to enhance a carrying performance and to have a high durability.

SUMMARY OF THE INVENTION

[0003] An object of the present invention is to provide a golf ball capable of giving a soft feeling of hitting the ball, and having a high resilience enough to enhance a carrying performance, and a high durability.

[0004] The present inventors have earnestly studied a soft golf ball including a solid core and a cover, and found that even if a deformed amount of a solid core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 6.5 mm, a golf ball having a high resilience, a low spin, a high hitting angle, a high carrying performance, and a high durability can be obtained by providing a high hardness cover layer which is made from a base resin containing an inorganic filler in an amount of 5 to 40 parts by weight on the basis of 100 parts by weight of the base resin and which has a Shore D hardness in a range of 66 to 80, wherein the high hardness cover layer is preferably taken as an outermost cover layer. On the basis of such knowledge, the present invention has been accomplished.

[0005] To achieve the above object, according to an aspect of the present invention, there is provided a golf ball including: a solid core; and a cover having one layer or two or more layers provided to directly cover the solid core or cover the solid core via an intermediate layer; wherein at least one layer of the cover is taken as a high hardness cover layer which is made from a base resin containing an inorganic filler in an amount of 5 to 40 parts by weight on the basis of 100 parts by weight of the base resin and which has a Shore D hardness in a range of 66 to 80.

[0006] The high hardness cover layer is preferably an outermost cover layer.

[0007] The base resin for forming the high hardness cover layer preferably has a Shore D hardness in a range of 65 or more.

[0008] The Shore D hardness of the high hardness cover layer is preferably higher than the Shore D hardness of the base resin by 1 or more.

[0009] The inorganic filler contained in the high hardness cover layer is preferably titanium dioxide and/or barium sulfate.

[0010] The high hardness cover layer preferably contains titanium dioxide as the inorganic filler in an amount of 2 parts by weight or more.

[0011] A deformed amount of the solid core, measured by applying a load of 980 N thereto, is preferably in a range of 4.0 to 6.5 mm.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be hereinafter described in detail.

[0013] A golf ball of the present invention is a solid golf ball including a solid core and a cover.

[0014] The solid core can be produced by vulcanizing a rubber composition. The rubber composition may contain a main rubber component, an unsaturated carboxylic acid and/or a metal salt thereof as a crosslinking agent, and an organic peroxide.

[0015] As the above-described main rubber component, there is preferably used polybutadiene, particularly, cis-1,4-polybutadiene. In this case, another diene based rubber, such as styrene-butadiene rubber (SBR), natural rubber, isoprene rubber, or ethylene-propylene-diene rubber (EPDM) may be suitably mixed with polybutadiene as a main component of the main rubber component, as needed.

[0016] Examples of the unsaturated carboxylic acids, each of which is usable as the crosslinking agent of the main rubber component, may include acrylic acid, metacrylic acid, maleic acid, fumaric acid. In particular, acrylic acid and metacrylic acid are preferably used.

[0017] Examples of the metal salts of unsaturated carboxylic acids may include zinc salts and magnesium salts of unsaturated aliphatic acids, for example, zinc metacrylate and zinc acrylate. In particular, zinc acrylate is preferably used.

[0018] The content of the unsaturated carboxylic acid and/or metal salt thereof may be set, on the basis of 100 parts (parts by weight, the same applying hereinafter) of the main rubber component, in a range of 10 parts or more, preferably, 15 parts or more, more preferably, 20 parts or more, with the upper limit being set in a range of 50 parts or less, preferably, 45 parts or less, more preferably, 40 parts or less, most preferably, 35 parts or less. If the content is excessively small, the resilience is reduced, while if excessively large, the solid core becomes excessively hard, thereby often causing undesirable player's feeling of hitting of the golf ball.

[0019] As the organic peroxide, there can be used a commercial product such as “Percumyl D” (sold by NOF CORPORATION), “Perhexa 3M” (sold by NOF CORPORATION), “Luperco 231XL” (sold by Elf Atochem Japan). Two kinds or more organic peroxides may be used in combination, as needed.

[0020] The content of the organic peroxide may be set, on the basis of 100 parts of the main rubber component, in a range of 0.1 part or more, preferably, 0.3 part or more, more preferably, 0.5 part or more, most preferably, 0.7 part or more, with the upper limit being set in a range of 5 parts or less, preferably, 4 parts or less, more preferably, 3 parts or less, most preferably, 2 parts or less. If the content is excessively large or small, the resilience, feeling of hitting the golf ball, and durability may not be obtained.

[0021] The rubber composition of the present invention may contain, in addition to the above-described essential components, an inorganic filler for adjusting a specific gravity of the rubber composition, as needed. Examples of the inorganic fillers may include zinc oxide, barium sulfate, and calcium carbonate. In order to obtain a suitable weight and a desirable resilience, the content of the inorganic filler may be set, on the basis of 100 parts of the main rubber component, in a range of 1 part or more, preferably, 3 parts or more, more preferably, 5 parts or more, most preferably, 7 parts or more, with the upper limit being set in a range of 60 parts or less, preferably, 50 parts or less, more preferably, 45 parts or less, most preferably, 40 parts or less.

[0022] An antioxidant may be further added to the rubber composition of the present invention, as needed. As the antioxidant, there can be used a commercial product such as “NOCRAC NS-6, NS-30” (sold by Ouchi-Sinko Chemical Industrial Co., Ltd.), or “Yoshinox 425” (Yoshitomi Pharmaceutical Co., Ltd.). In order to obtain desirable resilience and durability, the content of the antioxidant may be set, on the basis of 100 parts of the main rubber component, in a range of 0 part or more, preferably, 0.05 part or more, more preferably, 0.1 part or more, most preferably, 0.2 part or more, with the upper limit being set in a range of 3 parts or less, preferably, 2 parts or less, more preferably, 1 part or less, most preferably, 0.5 part or less.

[0023] The rubber composition of the present invention may contain an organic sulfur compound, as needed. Examples of the organic sulfur compounds may include thiophenol, thionaphthol, halogenated thiophenol, or metal salts thereof, more concretely, zinc salts of pentachlorothiophenol, pentafluorothiophenol, pent abromothiophenol, and parachlorothiophenol; and diphenyl polysulfide, dibenzil polysulfide, dibenzoil polysulfide, dibenzothiazoil polysulfide, and dithiobenzoil polysulfide, each of which has the sulfur number of 2 to 4. In particular, a zinc salt of pentachlorothiophenol or diphenyl disulfide is preferably used. The content of the organic sulfur compound may be set, on the basis of 100 parts of the main rubber component, in a range of 0.05 part or more, preferably, 0.1 part or more, more preferably, 0.2 part or more, with the upper limit being set in a range of 5 parts or less, preferably, 4 parts or less, more preferably, 3 parts or less, most preferably, 2.5 parts or less.

[0024] The solid core of the present invention can be formed by vulcanizing and hardening the above-described rubber composition by a known process. For example, a vulcanizing temperature may be set in a range of 100 to 200° C., and a vulcanizing time be set in a range of 10 to 40 min.

[0025] According to the present invention, the hardness of the solid core, which is expressed in a deformed amount of the solid core measured by applying a load of 980 N (100 kg) thereto, may be set in a range of 4.0 mm or more, preferably, 4.2 mm or more, more preferably, 4.3 mm or more, with the upper limit being set in a range of 6.5 mm or less, preferably, 6.0 mm or less, more preferably, 5.2 mm or less. If the flexural amount (deformed amount) is excessively small, the feeling of hitting the golf ball becomes harder, and particularly, the spin of the ball becomes excessively high at the time of long-shot with a driver when the ball is liable to be largely deformed, to reduce the carry of the ball, while if excessively large, the feeling of hitting the ball becomes dull, the carry of the ball is reduced because of the insufficient resilience of the ball, and the durability against cracking due to repeated hitting is degraded.

[0026] In addition, the deformed amount of the core can be determined by suitably selecting the kinds and amounts of components of the rubber composition and the vulcanizing condition.

[0027] The diameter of the solid core of the present invention may be set in a range of 38.0 mm or more, preferably, 38.5 mm or more, more preferably, 38.7 mm or more, most preferably, 38.9 mm or more, with the upper limit being set in a range of 41.0 mm or less, preferably, 40.7 mm or less, more preferably, 40.3 mm or less, most preferably, 40.1 mm or less.

[0028] The specific gravity of the solid core may be set in a range of 1.000 or more, preferably, 1.050 or more, more preferably, 1.100 or more, with the upper limit being set in a range of 1.300 or less, preferably, 1.250 or less, more preferably, 1.200 or less.

[0029] The solid core may be of one layer structure or a multi-layer structure having two or more layers insofar as the deformed amount of the solid core satisfy the above-described requirement thereof.

[0030] The cover provided to cover the core may be of a one-layer structure or a multi-layer structure having two or more layers. According to this embodiment, however, at least one layer, particularly, an outermost layer is made from a base resin which contains an inorganic filler in an amount of 5 to 40 parts by weight on the basis of 100 parts of the base resin and which has a Shore D hardness in a range of 66 to 80.

[0031] The base resin for forming the high hardness cover layer is preferably an ionomer resin, and preferably has a Shore D hardness in a range of 65 or more, more preferably, 66 or more.

[0032] Examples of the inorganic fillers contained in the base resin may include titanium dioxide and barium sulfate. The content of the inorganic filler may be set, on the basis of 100 parts of the base resin, in a range of 5 parts or more, preferably, 8 parts or more, more preferably, 10 parts or more, with the upper limit being set in a range of 40 parts or less, preferably, 38 parts or less, more preferably, 35 parts or less, most preferably, 30 parts or less. If the content of the inorganic filler is excessively small, the effect of the present invention cannot be sufficiently obtained, and therefore, the durability may be degraded, while if excessively large, the resilience may be reduced and the rate of occurrence of failures at the time of molding the base resin be increased. In addition, the content of titanium dioxide may be set, on the basis of 100 parts of the base resin, in a range of 2 parts or more, preferably, 3 parts or more.

[0033] A UV absorbent, an oxidation inhibitor, a dispersant, and a coloring agent can be added to the cover material, as needed. A specific gravity of the high hardness cover layer may be set in a range of 1.020 or more, preferably, 1.030 or more, more preferably, 1.040 or more, with the upper limit being set in a range of 1.110 or less, preferably, 1.090 or less.

[0034] According to the golf ball of the present invention, the Shore D hardness of the high hardness cover layer may be set in a range of 66 or more, preferably, 67 or more, more preferably, 68 or more, with the upper limit being set in a range of 80 or less, preferably, 78 or less, more preferably, 75 or less. If the Shore D hardness of the high hardness cover layer is excessively low, the resilience may become insufficient and the carrying performance may be degraded, while if excessively high, the durability may be degraded.

[0035] In this case, by adding the inorganic filler to the base resin, the Shore hardness of the high hardness cover layer becomes higher than the Shore D hardness of the base resin by 1 or more, particularly, 2 or more.

[0036] If the cover has a one-layer structure, then the cover is composed of the above-described high hardness cover layer, and if the cover has a multi-layer structure having two or more layers, then at least one layer, preferably, the outermost layer of the cover is taken as the high hardness cover layer. In this case, for the cover having the two or more layers, the hardness of each of the cover layers other than the high hardness cover layer is preferably lower than the hardness of the high hardness cover layer and higher than the surface hardness of the core. The base resin for forming the cover layers other than the high hardness cover layer may be a known cover material, for example, an ionomer resin, or a polyurethane based, polyamide based, or polyester based thermoplastic elastomer. These materials may be used singly or in combination of two or more kinds. As these ionomer resin and thermoplastic elastomer, commercial products can be used.

[0037] For the cover composed of only the single high hardness cover layer, a thickness of the high hardness cover layer may be set in a range of 1.0 mm or more, preferably, 1.1 mm or more, with the upper limit being set in a range of 2.3 mm or less, preferably, 2.2 mm or less, more preferably, 2.1 mm or less, most preferably, 2.0 mm or less. For the cover of the multi-layer structure having two or more layers, a thickness of the high hardness cover layer may be set in a range of 1.0 mm or more, preferably, 1.1 mm or more, with the upper limit being set in a range of 2.3 mm or less, preferably, 2.2 mm or less, more preferably, 2.1 mm or less, most preferably, 2.0 mm or less. The total thickness of the cover may be set in a range of 1.3 mm or more, preferably, 1.5 mm or more, with the upper limit being set in a range of 6.0 mm or less, preferably, 5.0 mm or less.

[0038] If the thickness of the high hardness cover layer is excessively thin, the durability may be degraded, while if excessively thick, the feeling of hitting may become hard or dull.

[0039] The cover of the golf ball of the present invention can be formed by a known process of putting the solid core in a specific mold for injection molding, and injection-molding the cover material. Alternatively, the cover can be formed by preparing a pair of cup-halves made from the cover material, putting the solid core covered with the cup-halves in a specific mold, and press-molding the resultant solid core covered with the cup-halves.

[0040] Like a general golf ball, the golf ball of the present invention has in the cover surface a large number of dimples. The total number of the dimples may be set in a range of 350 or more, preferably, 370 or more, more preferably, 390 or more, with the upper limit being set in a range of 500 or less, preferably, 480 or less, more preferably, 450 or less. As the geometrical arrangement of the dimples, there can be adopted an octahedron or icosahedron arrangement. The pattern of the dimple is not limited to a circular shape but may be a square, hexagonal, pentagonal, or triangular shape.

[0041] The golf ball of the present invention can be produced with its diameter and weight specified under a golf rule for golf games. Concretely, the diameter of the golf ball can be set in a range of 42.67 mm or more, with the upper limit being set in a range of 44.0 mm or less, preferably, 43.5 mm or less, more preferably, 43.0 mm or less, and the weight of the golf ball can be set in a range of 45.93 g or less, with the lower limit being set in a range of 44.5 g or more, preferably, 44.8 g or more, more preferably, 45.0 or more.

[0042] As described above, the present invention can provide a golf ball having a high carrying performance, a desirable very soft feeling of hitting, and an excellent durability against continuous hitting.

EXAMPLE

[0043] The present invention will be more clearly understood by way of, while not limited thereto, the following examples and comparative examples. In the examples, “parts” designate parts by weight.

Examples 1 to 4 and Comparative Examples 1 to 3

[0044] A two-piece solid golf ball including a solid core and a cover was produced from each of rubber compositions shown in Table 1 by a known process.

[0045] Each golf ball thus obtained was evaluated in terms of carrying performance, durability against continuous hitting, and feeling of hitting in accordance with the following manners. The results are shown in Table 1. It is to be noted that in Table 1, “Himilan” is an ionomer resin sold by Du Pont-Mitsui Polychemicals Co., Ltd. TABLE 1 Comparative Example Example 1 2 3 4 1 2 3 Composition Cis-1,4-Polybutadiene 100 100 100 100 100 100 100 of Core Zinc acrylate 22.8 21.5 17.0 18.3 22.8 27.3 24.2 (part by Zinc oxide 5 5 5 5 5 5 5 weight) Barium sulfate 16.2 16.7 18.8 18.2 4.8 18.0 23.3 Dicumyl peroxide 1.4 1.4 1.4 1.4 1.4 1.4 1.4 Physical Hardness of Core 4.5 4.8 5.5 5.5 4.5 3.5 4.2 Properties (deformed amount under 980N) of Core Composition Himilan 1605 50 50 50 of Cover Himilan 1706 50 (part by Himilan AM7317 50 50 weight) Himilan AM7318 50 50 Himilan AM7315 50 100 100 50 Barium sulfate 10 10 10 10 40 Titanium dioxide 4 4 4 4 4 4 4 Physical Hardness of Cover (Shore D) 69 68 69 69 67 64 67 Properties Base resin (with no additive) 67 66 67 67 64 64 67 of Cover Thickness (mm) of Cover 1.9 1.9 1.9 1.9 1.9 1.9 2.5 Data of Weight (g) of Core 45.3 45.3 45.3 45.3 45.3 45.3 45.3 Ball Outer diameter (mm) of Cover 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Carry Hitting angle (°) 12.2 12.3 12.7 12.6 12.0 11.8 12.0 HS40 Spin (rpm) 2680 2600 2370 2450 2720 2960 2710 Total carry (m) 196.3 196.3 196.3 196.3 192.3 195.7 193.0 Durability against Continuous Hitting ⊚ ⊚ ⊚ ⊚ ⊚ X X Felling of Hitting Soft Very Very Very Soft Hard Soft soft soft soft

[0046] Measurement of Carry:

[0047] The ball was hit with a hitting machine (sold by Miyamae Co., Ltd.), to which a driver with a loft angle of 10° (sold by Bridgestone Sports Co., Ltd.) was mounted, and the carry of the ball was measured.

[0048] Durability Against Continuous Hitting:

[0049] The durability against continuous hitting, which was performed by a rotary drum type continuous hitting machine, was evaluated.

[0050] ⊚: very good

[0051] ◯: good

[0052] ×: undesirable

[0053] Feeling of Hitting:

[0054] The feeling of hitting of the golf ball was evaluated by a function test performed by 10 of professional players and 10 of amateur players.

[0055] As is apparent from Table 1, the golf ball in Examples 1 to 4 is superior to the golf ball in Comparative Example 1 to 3 in terms of carrying performance, durability against continuous hitting, and feeling of hitting.

[0056] While the present invention has been described using specific terms, such description is for illustrative purposes only, and it is understood that changes and variations may be made without departing from the spirit of scope of the following claims. 

1. A golf ball comprising: a solid core; and a cover having one layer or two or more layers provided to directly cover said solid core or cover said solid core via an intermediate layer; wherein at least one layer of said cover is taken as a high hardness cover layer which is made from a base resin containing an inorganic filler in an amount of 5 to 40 parts by weight on the basis of 100 parts by weight of said base resin and which has a Shore D hardness in a range of 66 to
 80. 2. A golf ball according to claim 1, wherein said high hardness cover layer is an outermost cover layer.
 3. A golf ball according to claim 1 or 2, wherein said base resin for forming said high hardness cover layer has a Shore D hardness in a range of 65 or more.
 4. A golf ball according to any one of claims 1 to 3, wherein the Shore D hardness of said high hardness cover layer is higher than the Shore D hardness of said base resin by 1 or more.
 5. A golf ball according to any one of claims 1 to 4, wherein said inorganic filler contained in said high hardness cover layer is titanium dioxide and/or barium sulfate.
 6. A golf ball according to any one of claims 1 to 5, wherein said high hardness cover layer contains titanium dioxide as said inorganic filler in an amount of 2 parts by weight or more.
 7. A golf ball according to any one of claims 1 to 6, wherein a deformed amount of said solid core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 6.5 mm. 